Multiple-range sound-transmitting system



May 7, i929. w. HAHNEMANN MULTIPLE RANGE SOUND TRANSMITTING SYSTEM Filed May 14,. 1925 -tvPat-e-nted May 7,

UNITED 4STATES 1,111,529 PATENT OFFICE'.

. I l WATER OF KIEL, GERMANY, ASSIGNOB To SIGNAL GESELISCHAF T MIT BESCHRENKTER HAFTUNG, 0F KIEL, GERMANY.

ilumina-RANGE soUND-rnANsMrrTING SYSTEM.

Application led May 14, 1923. Serial No. 638,838.

My. invention is illustrated in the accom panying drawings, in which Figure 1 represents a system of resonance curves; and

. 5 Figure 2 shows diagrammatically one of the numerous forms in which my invention uniform quality frequencies at least within the range of 5O to 3000per second. If it is desired to use a single sound responsivev device at the sound receiving or sound transmitting end which is tuned and constructed so that it covers thisentire range with fair uniformity, a damping would be required which is much reater than unit and which, therefore, can e produced on y to a very small extent by radiation damping, even if such a tuned system constitutes av coupled twoor three-wave system. In systems used inthe present" day'practice, the radiation damping amounts to only about 0.1 'to 0.2. Therefore, very lai"- e friction damping must be employed in or er to make such instruments fairly responsive to all 'frequencies within the transmission range.

At the present day, in order to cover a large range of tone frequencies withone single instrument (either at the sound receiving or. sound transmitting side of the 35. system) it is thereforel possible to build such apparatus, such as microphones or telephones, only with a very .large friction damping, w ich is for instance' produced by mounting the dia hra-gm between rubber 4o cushions so that it Ibecomes imperfectly fas` tened. Therefore, the lar e damping, which must be inherent to these instruments in order to cover the entire range 0fl tone frequencies is not produced to a sufficient extent by radiation damping, and therefore, is

produced at the expense o etliciency.

The above statements -furnish an explanation Why at the present day so many com paratively cr-udely designed and built instruments appear to give such comparative good acoustic effects. Such instruments, for instance owing to the imperfect fastening of the diaphragm as explained above, have a great friction damping of their diaphragms 35 and reproduce all tone frequencies comparasurface, namely, at those points where the tively good but at a Very low eiciency,'that 1s say, they have a very small sound intensity.

Most acoustic devices for the purpose of sound reception and sound emission, such as microphones and telephones, employ diaphragms, practically all of which have, aside from their fundamental frequency, also overtone frequencies. By this characteristic feature the effect is automatically obtained that these diphragms cover a comparatively large portion of the entire tone frequency range and that they have a comparatively good .effect at a great many oints of their overtone frequencies are located.

I have attem ted--and Iam aware that others have ma e similar attempts-to construct lthe diaphragm such that a definite pre-arranged group of overtones is formed and I have coupled-.such a diaphragm with correspondingly tuned air chambers in order to obtain a good eciency at all of these overtone frequencies.' .A

Of course, a good eliiciency of such a device will be obtained only in case thel equation' exists for the sound receiver (microphone) radiation damping (dm) approximately=useful damping (dwf), or more correctly ex ressed: dmd+dfr'c=df. U35' ,v In case o a sound radiator (telephone.or` loud speaker) the equation must exist: radiation damping larger than or at least not too small compared with the remaining (friction) damping.

Of course, sound transmittin devices of this characteristic can be built, utv it is extremely difficult to properly arrange even only two or three of such frequency groups exactly as required, since in the construction of such a device extremely careful workmanship and experimentin with each individual diaphragm is require For this reason it lbecomes almost impossible to commercially manufacture such devices in quantities. Of

course,even. if three of such frequencies were grouped together with the greatest care, the l necessarily large range ofvtone frequencies, ordinarily used, would hardly be covered. l

I am aware that at the present day sound responsive devices of the above character have been constructed, which have good ei'n'- ciency, but which cover only a comparatively small range of frequencies. So far as I know a range of frequency in the proportion of 1 :2 110 addition to the proper selection of damping (for instance l000/sec.2000/sec.") has `been thus covered at a fairly good eliiciency.

The present invention proposes to solve the problem of' constructing sound apparatus,

having a good etiiciencythroughout the entire tone frequency range commonly used, by using such sound receivers (microphones or the like) and soundradiators (telephones or the like) correctly built as previously men-- also the coellicient of coupling between the several systemsmust be properly.selected. One must then, in case of sound receivers, tend to obtain the result that the energy transinitted from the radiating system (diaphragm) to the system coupled with it, constitutes an amount sufiicient-for good eiiiciencywcompared with the energy radiated by the radiating s stem (diaphragm). In case of sound sen ers the radiated energy (in the form of sound) must be large or at least comparable to the energy otherwise consumed in the coupled systems (for instance friction damping).

Since such instruments individually cover a comparatively small range of tone freuencies I attainthe necessary largerange or transmitting speech or music by using a' plurality of such correctly constructedl sound receivers and sound radiators each'being tuned for a different band of frequencies.

For example, one sound receiver may have' at good efficiency a range from 600 to 1200 periods, thenext' from 1200 to 2400 periods and so forth.

- It' is obvious that the final result will be thebetter the more of such diderently tuned systems of good efliciency are used.

I have shown 1n Figure 1 of the drawings v three resonance curves I, II and. III each -represemting the curve of a coupled system (acoustically coupled). In this case each individual portion of the coupled system is tuned to the frequency nr which results in the ytwo frequencies ofthe coupledI system n, and

n2. If a number of such coupled systems, each having a frequency range different from the others, are added and combined into one receiver or sender apparatus, the result will be arange of frequencies substantially covering the entire tone frequency range and in which at substantially all points of the range the sound is transmitted with good efficiency. As shown in Figure 1, the irst'range might cover frequencies from 600 to 1200, the secf ond range from 1200 to 2300 and the third range from 2300 to 4200 and so forth.

In Figure 2 Isha've illustrated in diagrammatic fashion( how a sound transmitting system of this character may be arranged in practice. While I have-shownlin this ligure only three devices each at the sound receiving and sound transmitting side of the system as an example, I do not wish to be understood to limit myself to a s ecic number of indi.-

vidual devices, since t eir number would obviously be determinedthrough the` purpose and result to be obtained.

Referring now to Figure 2, l, 2 and represent 'a'. .sound receiver for instance a microphone which is connected electricall to the main transmission line Z1, Zz-throug individual circuits to be,referred to herein- 1 after more specifically. Each micro' hone is suitably tuned acoustically .to a certaln range of .tone frequencies different from the range to which the other microphones are tuned, and in such manner that b the total number of microphones employe the entire range of tone frequencies is included which it is desired tocover. Thus each microphone may easily be designed to operate at the bestv possible efficiency within itsown small range.

Of course, instead of a microphone, any otherl suitable sound-receiver may be used as an equivalent.

As stated before, each microphone is connected to the main line Z1, l, -by means ofvan individual circuit connection. The microphones may be energized from a common'circuit, containing the directvc'urrent source ll--for instance a battery--bridged by a condenser 10. For each microphone a transformer la, 2a, 3a respectively is provided, -ivhose secondary coil is connected to an individual transmitting circuit by.Y` which,y it is connected to the common main line. I propose, in addition to acoustically tuning each microphone to theV desired individual range of frequencies, to also electrically'dimension the above mentioned individual circuit connection between the microphone and the main loo line to its particular *range of frequencies. 4

This electric dimensioning may comprise any -suitable expedient well known in the art,

such as so-called filter circuits which for instance readily permit the passage of currents within a definite range of frequencies, but which offer hig'i impedance to currents of all other freque iesoutside of the range for whichthey are designed, or also such as simple tuned circuits. Thus, for instance the microphone 1 (which may cover the lower frequencies) may be 'connected to the main Z1, Z2 through its transformer l and a circuit containing a number of filter circuits having the inductances 4 and 5 and the capacities 6 and 7, arranged as shown, whereasmicro phone 2 (middle frequency range) may be connected to the main line through simple tunedcircuits'having the inductance 8 and the capacity 9 arranged as shown. Microphone 3 (highest range) may be connected to the main line in a fashion similar to the connection of microphone 1., but in this case the capacities 14, 15 are connected in series and the inductances 12, 13 are connected in shunt, in order to suppress the lower frequencies in this circuit.

The sound transmitting or, radiating end"Y which may re resent a loud speaker maybe arranged as fo lows v Three telephones 16, 17 and 18 are arranged around a common tone chamber 19. The diaphragms of these telephones are indicated at v 20 and their energizing coils are denoted by 21. Each telephone is provided With a specific individual tone chamber 22 and each telephone diaphragm 20 with its pertaining tone chamber 22-is tuned 'to a certain frequency different from the frequencies to to which the other .diaphragms and pertaining chambers are tuned, so that vfor instance in this case for each telephone an acousti` cally coupled system is produced (consisting of a diaphragm and a tone chamber) Which covers a range of frequencies such as is indicated in Figure 1. The main chamber 19 may o en into a horn 23, the shape of Which .may a so be formed suitable with relation to the main chamber 19 so as to produce the best possible eiiiciency.

' The energizing coils 21 of the individual 25 are arranged in these circuits for instance,

all in a similar fashion, although they may of course be arranged for each circuit in any other suitable manner Well known in the art so as to produce the desired electrical filtering or tuning effect.

I have shown in Figure 2 the three telephones, in other Words, a plurality of sound radiators, arranged so that their sound ema# nates through a common horn. If desired it is, of course, possible to also have an indi#` vidual horn for each telephone the same as at the other end' of the system an independent individual microphone is shown for each range of tone frequencies. Likewise instead of aving a number of independently arranged microphones they all may be arranged to receive the sound from a common Ahorn or `speaking tube such as `is shown at 23 at the radiating end of the system. Also, if expedient, the number of' individual sound devices at one end of the system, may notibe 'eqpal to thatat the otherend of the system,

ese modifications are considered as being "equivalents and intended to be within the -into oscillating electrical energy, may be entirely Within the discretion of those skilled in the art,and I have, therefore, omitted in thedrawings a direct conductive connect-ion between the sound receiving and sound radiatin end of the system, the gap, being indicate by the letter ai, denoting that the transmission may be either directly, such as by direct conductors, or indirectly such as by inductive transformation or by radio transmission or the like, the mode of transmitting the oscillating electrical energy having no bearing on the operation and function of the present invention. Also if desired, only one of the two ends'of the system shown in Fig-l ure 2 may be `used alone, that is to say, for instance the oscillating electrical energy into which the sound received| by the microphones is transformed, may be conveyed by lines Z1, Z2 to any 'device suited for; receiving and utilizing such energy. i

l claim .mittinff system a plurality of individual independent sound responsive devices actuated simultaneously and located to be responsivel for ythe same sound (Waves, each being electrica'lly and acoustally dimensioned to a definite different portion of the entire range of sound frequencies to be covered, to the exclusion of all other portions of said range.

2. ln a multiple range electric sound transmitting system a plurality of sound responsive devices actuated simultaneously and located to be responsive for the same sound Waves, comprising independent individual sound receivers and sound radiators arranged at the two ends of the system respectively, each -receiver and radiator comprising a plurality of mechanically coupled oscillatory structures, the devices at each end being each electrically and acoustically dimensioned for a definite different portion of the entire lrange of sound frequenciesto be covered, each device excluding all other portions of said range and a common electrical transmitting con nection between` the sound receivers. and

radiators.

3. In amultiplc range'electric sound transmitting vsystem a plurality of sound respon- .sive devices actuated simultaneously, comprising independent individual sound receivers and sound radiators arrangedat the It'Wo ends of the system respectively, each :fe--

ceiver and radiator comprising a plurality of mechanically coupled voscillatory strucy tures, the devices at each end being each electrically and acousticallydimensioned for a tical transmitting effect ofthe individual de# pled oscillatory structures, the4 individual vices.

4. vIn a multiple range electric sound transmittino' system a plurality of individual independent sound res onsivedevices actuated simultaneously and ocated to be responsive for the same sound Waves, each being 'elec-` trically and acoustically dimensioned to a definite 'different portion of the entire range of soundfrequencies to be covered, to the exclusion of all other portions of said range, the

said sound "responsive devices consisting of mechanical vibratory systems and electrical circuits, eachl 'of said mechanical stems comprising a plurality of mechanical y coustructures of any one system having the same natural frequency before coupling. l

f 5. In a multiple range electric sound transmitting vsystem a plurality of individual in# dependent sound responsive devices actuated simultaneously and located to beresponsive `for the same sound Waves, each bein electrically and acoustically dimensione delinite different portion of the entire range A of sound frequencies to be covered, to the extoa clusion of all other portions of said range, the said sound responsive devices consisting of mechanical vibratory systems and electrical circuits, each of said mechanical s stems comprising a plurality of mechanica y @coul pled oscillatory structures;A the individual structures of any one system having thesame natural frequency before coupling,an" thesaid electrical circuits consisting ofglter cir cuits. f i

WALTER' HAHNEMn-i, 

